Rex Sole

Rex Sole, Glyptocephalus zachirus

Rex Sole (1)

Rex Sole (2)

Rex Sole, Glyptocephalus zachirus.  Commercial fish courtesy of the Ranch 99 Market, San Diego, July 2012. Length: 37 cm (15 inches).

The Rex Sole, Glyptocephalus zachirus, is a member of the Righteye Flounder or Pleuronectidae Family, and known in Mexico as platija rey. Globally, there are three species in the genus Glyptocephalus, of which one is found in Mexican waters, this fish from of the Pacific Ocean.

The Rex Sole has an elongated oval fusiform compressed body with a depth that is 29% to 33% of standard length. They are uniformly grayish light brown on their eyed-side and off-white on their blind side. Their head has a pronounced hump around the top eye and a small oblique mouth that ends before the modestly-sized and closely-set eyes. Their anal fin has 78 to 93 rays; their caudal fin is rounded; their dorsal fin originates in the middle of the top eye and has 87 to 110 rays; and the pectoral fins are exceedingly long on the eyed-side, a key to identification. They are covered with small scales and their lateral line is straight but slightly curved over their pectoral fin.

The Rex Sole is a demersal species found over and within sandy and muddy bottoms at depths up to 1,130 m (3,700 feet). They reach a maximum of 60 cm (23 inches) in length and 1.8 kg (4 lbs 0 inches) in weight. They are very slow growing. They are a migratory species found in shallow waters during the summer and in deeper waters in winter when spawning occurs. They are opportunistic well-camouflaged ambush predators that lie in wait half-submerged on the ocean floor consuming crustaceans (clams, crabs, polychaetes, and shrimp). They have a lifespan of up to twenty-four years. The Rex Sole is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity, movement patterns, diet, habitat use, and reproduction.

The Rex Sole is a resident of Mexican waters of the Pacific Ocean but has a limited distribution being found from Cedros Island, Baja California, northward along the central and northwest coasts of Baja.

The Rex Sole is a straightforward identification that cannot be confused with any other species due to its exceedingly long pectoral fins.

From a conservation perspective the Rex Sole has not been formally evaluated. They are fished commercially via trawler and comprise a major part of the flatfish trawl fishery north of California. They are heavily regulated; in the Bering Sea they are fished with special modified “Bering Sea Flatfish Gear” that consists of sweeps raised off the seafloor by bobbins spaced at 30m (100 feet) intervals to herd flatfish into relatively small nets. This technique dramatically reduces the adverse effects of fishing on seafloor habitat. Fish are processed on-board and immediately frozen, then processed further onshore. They have become an excellent substitute for the once common Sanddab as they have tender white finely-grained meat with a mild flavor. They are normally sold whole, fresh or frozen, or “pan ready” (with their head, innards, scales, tail, and fins removed as they are difficult to fillet). Many are processed into fertilizer. They are sold in great abundance in the ethnic fish markets of California. Some of the highly competitive San Diego based Asian markets have been known to substitute Flathead Sole, Hippoglossoides elassodon, for Rex Sole offering such “Rex Sole” at discounted prices. Efforts to farm this species have been unsuccessful primarily due to its slow growth.